Learn Functional Programming in PHP/

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Value Objects

Value Objects

Learn about value objects and their implications.

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Overview

A value object is an abstract data type wherein each object represents an entity: the value. The grounds for a comparison of value objects is their value, not the identity of the object. The code below demonstrates this.

Code example

PHP
<?php
class HttpMessage
{
  private int $code;
  private string $response;
  public function __construct(int $code, string $response)
  {
    $this->code     = $code;
    $this->response = $response;
  }
  public function verify(HttpMessage $message) : bool
  {
    return $this->response == $message->response &&
      $this->code == $message->code;
  }
  public function newMessage(int $code, string $response) : HttpMessage
  {
    $newMessage           = clone $this;
    $newMessage->code     = $code;
    $newMessage->response = $response;
    return $newMessage;
  }
}
$ok = new HttpMessage(200, 'OK');
$created = $ok->newMessage(201, 'OK');
echo $ok->verify($created) ?
  'Value objects are equal' :
  'Value objects are not equal';

The class above is instantiable as an HTTP message value object. It ...